Referring to FIG. 1, there is shown a schematic view illustrating a general tape travelling system of a VCR. As shown in this drawing, a video tape is moved from a supply reel 6 to a take-up reel 7.
Namely, the video tape wound around the supply reel 6 is first moved through an inlet tape guide 2 and a supply loading post 8 to a rotatable head drum 1 to which recording and reproduction heads (not shown) are mounted. The recording and reproduction heads are adapted to record a video signal on the video tape and reproduce the video signal recorded thereon, respectively. While travelling along the head drum 1, the video tape is transferred to the take-up reel 7 through a take-up loading post 9, a capstan 5 and an outlet tape guide 4, the capstan 5 being in contact with a pinch roller 3.
Referring to FIG. 4, there is shown a schematic block diagram of a general high definition television (referred to hereinafter as HDTV) system. In a transmission part, a video signal from a camera is encoded by an encoder 12 for data compression thereof. The compressed data is transformed into a transmission format and then sent through a transmitter 13 to a transmitting antenna 14.
In a reception part, a video signal received through a receiving antenna 15 is detected by a receiver 16 and then decoded by a decoder 17 for data expansion thereof. The expanded video signal is displayed through a monitor 18. The video signal detected by the receiver 16 can also be recorded by a conventional digital VCR 19.
Referring to FIG. 5, there is shown a detailed block diagram of the conventional digital VCR 19. In a recording mode, the video signal from the receiver 16 in the HDTV system is received by an interface 21 and then interleaved by an interleaver 22 for error correction thereof. A recording formatter 23 is provided in the digital VCR 19 to transform the interleaved signal from the interleaver 22 into a desired recording format. A modulator 24 is adapted to modulate an output signal from the recording formatter 23. An output signal from the modulator 24 is amplified by a predetermined level by a recording amplifier 25 and then recorded on a video tape 26.
In a playback mode, a reproduction amplifier/equalizer circuit 31 amplifies the video signal recorded on the video tape 26 by a predetermined level and compensates for a distortion of the amplified signal. A synchronous signal detector 32 is adapted to detect a synchronous signal from the compensated signal from the reproduction amplifier/equalizer circuit 31 to stabilize a reproduction operation. An output signal from the synchronous signal detector 32 is rearranged into its original format by a reproduction formatter 33 and then demodulated by a demodulator 34. The demodulated signal from the demodulator 34 is deinterleaved by a deinterleaver 35 and then outputted through the interface 21 to the receiver 16 in the HDTV system.
In the recording and playback modes, a capstan motor 28 is rotated under a control of a capstan motor controller 27 to drive the capstan 5. The video tape 26 is moved as the capstan 5 is driven. Also, a drum motor 30 is rotated under a control of a drum motor controller 29 to drive the head drum 1. As a result, normal recording, normal playback or speed change playback is performed as the head drum 1 is driven.
The operation of the digital VCR with the above-mentioned construction will hereinafter be described with reference to FIG. 2 and FIGS. 3A to 3C.
FIG. 2 is a view illustrating a recording format of the video tape 26 in accordance with the prior art, FIG. 3A is a view illustrating a head trace of the video tape 26 in a still playback mode in accordance with the prior art, FIG. 3B is a view illustrating a head trace of the video tape 26 in a fast forward playback mode in accordance with the prior art and FIG. 3C is a view illustrating a head trace of the video tape 26 in a fast reverse playback mode in accordance with the prior art.
When moving along the head drum 1, the video tape 26 is wound on the head drum 1 in the order of 180.degree.. Under this condition, data is alternately recorded and reproduced on/from the video tape 26 by the recording and reproduction heads (not shown). The recording and reproduction heads have an azimuth angle of about 6.degree. with respect to each other for prevention of an interference in the data recording and reproduction.
In FIG. 2, each video track has an angle of inclination of 5.degree. 58' 9.9" to a head travelling direction in a helical manner. In such a helical manner, the video signal is recorded in the unit of field on each track of the video tape 26. In the playback mode, the capstan motor 28 is rotated under the control of the capstan motor controller 27 so that a travelling speed of the video tape 26 can be varied. Also, the drum motor 30 is rotated under the control of the drum motor controller 29 so that the reproduction of the video signal from the video tape 26 can selectively be performed in the still, fast forward and fast reverse playback modes as shown in FIGS. 3A to 3C.
In the normal playback mode, a relative speed of the drum 1 and the video tape 26 is 5.8 m/s and a travelling speed of the video tape 26 is 33.55 mm/s.
In the speed change playback mode, the drum 1 is rotated at a fixed speed under the control of the drum motor controller 29, whereas the rotation speed of the capstan motor 28 is varied under the control of the capstan motor controller 27 to adjust the travelling speed of the video tape 26.
In the still playback mode, the video signal is reproduced under the condition that the video tape 26 is stopped. In this case, a scanning point of the reproduction head misses somewhat the corresponding track of the video tape 26 as shown in FIG. 3A, resulting in noise being mixed with a reproduced picture. In the fast forward and reverse playback modes as shown in FIGS. 3B and 3C, the travelling speed of the video tape 26 is seven times that of the normal playback mode.
In the general HDTV system, intra-frame and inter-frame coding processes are performed for the data compression in the transmission part. The intra-frame coding is to compress data in one frame, whereas the inter-frame coding is to compress data according to a difference between the adjacent frames. The compressed data is recorded on the video tape 26. In this connection, a video field seen at the camera 11 or the monitor 18 is different from that at the transmitter 13 or the receiver 16.
The compressed data from the receiver 16 is recorded in the digital VCR 19. As a result, one field of the data recorded in the digital VCR 19 may be smaller or larger than that on the monitor 18 according to a compressed degree. Namely, one video field recorded on the video tape is not the same as that on a screen of the monitor 18.
For this reason, in the digital VCR, a video picture cannot be formed by a reproduction of only a part of one field such as a fast reproduction of a VHS system. Also, the video picture cannot be reproduced as it is, in the case where the VCR skips even one frame among inter-frame coded data. Further, in the HDTV system, data of a first line on the data field may be not exactly in accord with a start point of the upper left side of the screen. Moreover, in the HDTV system, the video signal is mainly compressed by the inter-frame coding, which applies a lot of restrictions for editing and the speed change playback of the digital VCR. Also, the intra-frame coding is performed only in a video variation.
As a result, the conventional digital VCR is desirable to perform the still playback mode and a slow playback mode of the video signal from the HDTV system, but has the disadvantage that it cannot perform the fast forward and reverse playback modes of the video signal from the HDTV system.